The present invention relates to the general field of controlling the orientation of the fan blades of a turboprop unit.
A preferred field of application of the invention is that of dual propeller airplane turboprops.
A dual propeller airplane turboprop comprises a turbine with two counter-rotating rotors each driving an unshrouded fan blade set. In this type of airplane engine, the orientation of the fan blades (also called pitch control) constitutes one of the parameters allowing the engine thrust to be managed.
French patent application no. 10 51458 filed on 1 Mar. 2010 by the Applicant describes a system for controlling the orientation of the fan blades of such a turboprop unit. In this document, each blade is coupled, for control of its orientation, to a blade root support mounted pivotably on a rotating ring by means of a bevel gearset, one pinion of this gearset being supported by the blade root support and the other pinion bearing a counterweight. A cylinder centered on the axis of rotation of the rotating ring and rotating integrally with the turbine rotor is connected to each counterweight through a radial connecting rod. By actuating the cylinder, the connecting rods act on the counterweights according to the rod-and-crank principle in order to bring about synchronized rotation of the blade roots.
Such a control system has numerous advantages. In particular, it is reliable and light because it has relatively few parts compared to prior art control systems.
The connecting rods of this system extend radially from the cylinder to the blade root supports. Also, some of these connecting rods must pass through an oil chamber wherein several ball bearings of the turboprop are installed. This is particularly the case for the connecting rods of the control system for the upstream blade set.
Now these oil chambers are rotating, such that the oil that is present is subjected to a centrifugal force. Consequently, in order to avoid any oil leak to the outside it is necessary to seal the passage through the walls of these oil chambers by the control system connecting rods.